The present invention relates to a composition, preferably a solution, for planarization of aluminum surfaces in the fabrication of semiconductor devices. More particularly, the present invention relates to compositions compatible with fixed abrasive articles for use in planarization of aluminum surfaces and methods of using such compositions.
During wafer fabrication of semiconductor devices, various surfaces are formed. Many of such surfaces do not have uniform height, and therefore, the wafer thickness is also non-uniform. Further, surfaces may have defects such as crystal lattice damage, scratches, roughness, or embedded particles of dirt or dust. For various fabrication processes to be performed, such as lithography and etching, height non-uniformities and defects at the surface of the wafer must be reduced or eliminated. Various planarization techniques are available to provide such reduction and/or elimination. One such planarization technique includes chemical-mechanical polishing (abbreviated herein as xe2x80x9cCMPxe2x80x9d).
The method of CMP is used to achieve a planar surface over the entire chip and wafer, sometimes referred to as xe2x80x9cglobal planarity.xe2x80x9d Conventionally, the process of CMP involves a wafer holder that holds a wafer. An abrasive slurry is applied so that it contacts the interface of the wafer and the polishing pad. A table or platen has a polishing pad thereon. The polishing pad is applied to the wafer at a certain pressure to perform the planarization. At least one of the wafer and a polishing pad are set in motion relative to the other. In some CMP processes, the wafer holder may or may not rotate, the table or platen may or may not rotate and/or the platen may be moved in a linear motion as opposed to rotating. There are numerous types of planarization units available which perform the process in different manners.
The use of abrasive slurries in wafer fabrication has proven problematic for several reasons. First, because abrasive slurries that contain a plurality of abrasive particles xe2x80x9cin solution,xe2x80x9d tend to be unstable. In particular, not only do the abrasive particles settle, the abrasive particles also tend to agglomerate, both phenomenon resulting in a nonuniform slurry composition. This, in turn, creates wide variability in the polishing results. Second, it is known within the art that the composition of the slurry tends to be very specific with the desired chemical-mechanical polishing process, i.e., one slurry may not be suitable for a variety of CMP processes. Further, conventional CMP slurries typically do not work well with fixed abrasive CMP processes, for example, in aluminum surface planarization.
Further, conventional polishing pads also pose planarization difficulties. Such pads may glaze, or become embedded with debris, during polishing. This requires the pads to be conditioned such that the pads can be reused. Conditioning typically involves removal of the debris from the polishing pad using mechanical means with or without application of a solution. Conditioned pads typically leads to subsequent unpredictable CMP results because of the unpredictability in removal of debris from the pad itself during conditioning.
For the above reasons, there is a continuing need to provide a CMP using fixed abrasives and solutions compatible therewith in polishing aluminum. For example, conventional abrasive slurries are typically incompatible with fixed abrasive articles for CMP processes. This is particularly true with respect to alumimum-containing surface CMP processes, where aluminum can be present at about 50 atomic percent or more. The present invention as described below provides such improvements and overcomes the problems described above and those problems which will become apparent to one skilled in the art from the detailed description provided below.
One aspect of the present invention provides a composition compatible with a fixed abrasive article suitable for use in planarization of an aluminum-containing surface in the fabrication of semiconductor devices. Preferably, the composition is essentially abrasive particle-free from the stand point that the composition does not contain abrasive particles prior to its addition to the planarization process.
As used herein, xe2x80x9caluminum-containing surfacexe2x80x9d refers to an exposed region having aluminum present in an atomic amount of at least about 50% of the composition of the region, which may be provided as a layer, film, coating, etc. to be polishing or planarized in accordance with the present invention. The surface may consist essentially of elemental aluminum or an aluminum alloy.
Another aspect of the present invention provides a planarization method that includes positioning an aluminum-containing surface of a wafer surface to interface with a fixed abrasive article; supplying an aluminum CMP composition in proximity to the interface; and planarizing the wafer surface using the fixed abrasive and the aluminum CMP composition, the aluminum CMP composition comprising a surfactant, a complexant, and an oxidant, wherein the composition has a pH of less than about 10.
Yet another aspect of the present invention provides a planarization method for use in forming an interconnect. Preferably, the method includes providing a wafer having a patterned dielectric layer formed thereon and an aluminum-containing layer formed over the patterned dielectric layer; positioning a fixed abrasive for contact with the aluminum-containing layer; providing a composition in proximity to the contact between the fixed abrasive and the metal layer, wherein the composition comprises a surfactant, a complexant, and about 0.5% to about 15% by volume of an oxidant, wherein the composition has a pH of less than about 10; and planarizing the aluminum-containing layer using the fixed abrasive and the composition.
Yet a further aspect of the present invention provides a planarization method including providing a substrate assembly including at least one region of a aluminum-containing metal; providing a fixed abrasive; providing a composition at an interface between the at least one region of aluminum-containing metal and the fixed abrasive, wherein the composition comprises a surfactant, a complexant, and an oxidant, wherein the composition has a pH of about 1 to about 10; and planarizing the at least one region of aluminum-containing metal using the fixed abrasive and the composition.
In one embodiment of any of the methods in accordance with the present invention, the composition preferably has a pH of less than about 7.0, more preferably from about 3.0 to about 5.0. In another embodiment of any of the methods above, the composition preferably has a pH of about 6.0 to about 8.0.
In any of the methods in accordance with the present invention, the aluminum-containing surface preferably aluminum in a molar amount of about 50% or more. The aluminum-containing surface may include elemental aluminum or it may include an aluminum alloy.
In any of the methods in accordance with the present invention, the fixed abrasive preferably includes a plurality of abrasive particles, wherein a majority of the plurality of abrasive particles include SiO2. Preferably, the fixed abrasive comprises a majority of SiO2 abrasive particles and the aluminum CMP composition has a pH of less than about 8.
In any of the methods in accordance with the present invention, the fixed abrasive includes an elongated fixed abrasive capable of planarizing the aluminum-containing surface on a first wafer with a first portion on the elongated fixed abrasive and an aluminum-containing surface on a second wafer with a second portion on the elongated fixed abrasive.
Any of the CMP methods in accordance with the present invention are preferably accomplished at a temperature of about 24xc2x0 C. or less.
Preferably, the oxidant is present in the composition in an amount of about 0.5% to about 15% by volume, wherein the oxidant is preferably selected from the group consisting of Fe(NO3)2, KMnO4, H2O2, KNO3, HNO3, KIO3, ammonium persulfate, ammonium molybdate, and a combination thereof.
Preferably, the surfactant is present in the composition in an amount 1% to about 10% by volume wherein the surfactant is preferably selected from the group consisting of polyethylene glycol, polyoxyethylene ether, glycerol, polypropylene glycol, and a combination thereof.
Preferably, the complexant is present in the composition in an amount of about 1% to about 10% by weight, wherein the complexant is preferably selected from the group consisting of triethanolamine, ethylenediamine, ammonium citrate, ammonium phosphate, ammonium oxalate, ammonium carbonate, and a combination thereof.
The composition may further include an optional additive selected from the group consisting of a thickener, a buffering agent, and a combination thereof. If present, the thickener is in an amount sufficient to achieve a viscosity of the composition of about 10 centipoise to about 20 centipoise at ambient temperature. If present, the buffering agent can be selected from the group consisting of potassium hydrogen phthalate, ammonium salts (e.g., ammonium citrate, ammonium phosphate, and the like), and a combination thereof.
The composition may further include an aluminum corrosion inhibitor comprising from about 0.01% to about 2% by weight. Preferably, the aluminum corrosion inhibitor is selected from the group consisting of a phosphate, a polyphosphate, a silicate, and combination thereof.
Yet a further aspect of the present invention provides a composition consisting essentially of a surfactant in an amount of about 1% to about 10% by volume; a complexant in an amount of about 1% to about 10% by volume; and an oxidant in an amount of about 0.5% to about 15% by volume, wherein the composition has a pH of less than about 10 and is effective to planarize an aluminum-containing surface in the presence of a fixed abrasive. The composition may further include an optional agent selected from the group consisting of a buffering agent; a thickener; and a aluminum corrosion inhibitor.
As used herein, xe2x80x9csurfactantxe2x80x9d refers to a compound that reduces surface tension when dissolved in water or aqueous solutions, or which reduces interfacial tension between two liquids, or between a liquid and a solid. Conventional surfactants are categorized based on the nature of the solubilizing group found in the compound and are typically categorized as an anionic surfactant, a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant.
As used herein, xe2x80x9ccomplexantxe2x80x9d refers to a compound containing at least one donor atom capable of combining with a metal ion to form a complex having properties different from those present in either the original complexant or ion, such as a cyclic structure.
As used herein, xe2x80x9coxidantxe2x80x9d refers to a compound including at least one element from Group 1 of the Periodic Table combined with at least one oxygen atom.
As used herein, xe2x80x9cabrasive articlexe2x80x9d and xe2x80x9cfixed abrasivexe2x80x9d each refer to a structure which includes a plurality of abrasive particles dispersed within a binder adhered to at least one surface of a backing material.
As used herein, xe2x80x9cchemical-mechanical polishingxe2x80x9d and xe2x80x9cCMPxe2x80x9d refer to a dual mechanism having both a chemical component and a mechanical component, wherein corrosion chemistry and fracture mechanics both play a roll in wafer polishing.
Another aspect of the present invention provides a method of using a fixed abrasive in a CMP process for semiconductor fabrication.